A substrate processing apparatus functions to perform processing such as forming and improving a film on a substrate such as a semiconductor substrate or a glass substrate. Ozone is frequently used for the processing such as forming and improving the film. As a most generally used system of generating the ozone, a system using a silent discharge is given as an example.
In the discharge under the atmospheric pressure, usually non-steady discharge (non-arc discharge and non-thermal plasma) is used. The non-steady discharge is used for the reason that there is a fear that through a glow discharge and an arc discharge, a discharge breakdown (ignition) in an atmospheric pressure develops into a thermal breakdown of an apparatus, to make a steady discharge difficult to be used. The silent discharge is a discharge phenomenon observed under atmospheric pressure, in applying a voltage between electrodes where dielectric material is inserted, and the silent discharge becomes a non-steady discharge by the insertion of the dielectric material. Ozone is generated by utilizing the aforementioned discharge. In an ozone generator utilizing the silent discharge, specifically, as shown in FIG. 21, a dielectric material 2 is provided in one (FIG. 21A) or both (FIG. 21B) of a pair of parallel plate electrodes 1 and 1, and by impressing AC high voltage between the electrodes 1 and 1, a plasma discharge is intermittently caused between the electrodes 1 and 1 in the atmospheric pressure. Then, by passing oxygen O2 or dry air in the discharge atmosphere, ozone O3 is generated by utilizing a high energy electron of plasma, and a mixed gas (O2+O3) is obtained.
Also, in order to generate ozone, a creeping discharge which is one type of the silent discharge is sometimes used. As shown in FIG. 22, the creeping discharge is provided, with the dielectric material 3 put between a dielectric electrode 4 becoming a planar electrode at one side and a discharge electrode 5 becoming a line electrode at the other side. Then, AC high voltage is applied between the both electrodes 4 and 5 by an AC high voltage power source 6, so as to discharge between the discharge electrode 5 and the dielectric material 3. Then, the ozone O3 can be generated by feeding oxygen O3 or dry air in the discharge atmosphere 7.
The aforementioned silent discharge system has a simple structure such that a high voltage AC power source of 20 to 10000 Hz may be used as a power source, and it is necessary only to insert the dielectric material between the electrodes at a discharge part, and embed the electrodes in the dielectric material, and therefore the silent discharge system is exclusively utilized in the ozone generator.
As a conventional technique related to such a silent discharge, for example, the technique recited in the patent document 1 is known. In this technique, granules are formed by covering entire surface of a conductor with an insulating material, and inter-electrodes of electrode pairs is packed with such granules, so that the conductor in the granules forms a small electrode, and the insulating material constitutes a dielectric barrier. Dielectric barrier discharge changes the gas into plasma in a gap between granules. Since each gap between granules is small, even the gas with large discharge starting voltage such as oxygen and nitrogen is capable of generating a uniform glow discharge with an extremely small application power, and plasma and ozone are thereby generated.    Patent document 1: Japanese Patent Laid-open No. 8-321397